Outlook Client do not display content and ribbon when selected emails and calendars are popped out.

For the past week, I have experience Outlook not displaying content and ribbon when selected emails and calendar items are popped out.  The space where ribbon and content are displayed are blank!

Have tried various suggestions from Microsoft fixes like disabling Add-ons (in Options) but sometimes these steps work but most of the time they do not work.

Please help if any one can provide a solution or work around.

THanks

Amir